What Does Pressure In The Eyes And Head Indicate?

I suffer from pressure in my head and my eyes, sometimes it starts when I eat, sometimes it starts for no reason, It affects my ability to even function, my ability to think clearly, difficulty with wearing my contacts, but also can t go without my contacts for more than a couple of hours. I also have a very stiff neck and difficulty in swallowing. I have had many blood tests and several brain MRI s and one cervical MRI. I have been to throat doctors, neurologist, eye doctor, etc., and no one knows what is wrong.